This invention relates to a linkage for connecting a brake cable to a lever of an actuator for moving first and second brake shoes into engagement with a drum in drum-in-hat park brake.
In a vehicle having four wheel disc brakes an overall cost saving may be achieved through the use of a drum-in-hat parking brake such as disclosed in U.S. Pat. No. 5,180,037 as many of the structural components for a conventional service brake may be used in a parking brake. In a study of parking brakes, it was summarized that less than twenty five precent of drivers effect a parking brake application on a regular basis and the use of a parking brake was even less in vehicles having an automatic transmissions. With such limited use, an initial thickness of the material of friction members for a parking brake remain essentially the same over the life of a vehicle. It is common practice to develop a typical high coefficient of friction for a friction lining for a parking brake as the coefficient of friction between the friction pads and drum is needed to hold a vehicle stationary in a parking brake application. The coefficient of friction for the friction pads being derived from a composition of materials mainly consisting of metal oxides, ceramic particles, carbon particles, fibers and other materials retained in a phenolic matrix. The relative limited wear is not unexpected, as a vehicle is stationary when a parking brake application is applied and as a result frictional wear normally does not occur. However, current safety standards require a park brake to also be capable of functioning as an emergency brake and have an ability to achieve a minimum of six rolling stops from a speed of 18.6 miles per hour. In order to meet this requirement, it is not uncommon for an actuation force of approximately 100 Kg must be applied to bring brake shoes into engagement with a drum.
It is not uncommon for the drum-in-hat parking brake to be assembled at one place and later installed on a vehicle in another location through a brake cable connection such as disclosed in U.S. Pat. No. 5,174,170 or U.S. patent application Ser. No. 10/171,142 filed Jun. 13, 2002. Since it may be difficult and time consuming to install a brake cable to the actuator on an assembly line as such assembly is essentially a blind entry, it has been suggested that a stub linkage be provided with a drum-in-hat assembly the end thereof later joined to a brake cable by a crimp connection. Unfortunately the stub linkage and crimp connection can add cost of the overall brake assembly and as a result customers would prefer a different solution to this situation. A linkage as disclosed in U.S. patent application Ser. No. 10/323,321 addresses and provides a solution to some of the problems in the prior art type connections but requires certain dexterity to join the linkage to a brake cable.
A primary object of the present invention is to provide a simple low cost linkage for joining a brake cable to an actuator in a drum-in-hat park brake.
According to this invention, in a drum-in-hat park brake assembly for a vehicle having a first brake shoe and a second brake shoe that are respectively retained on a backing plate that is secured to said vehicle. The first brake shoe and said second brake shoe each have a first web with a first engagement end and a second engagement end. The first engagement end of each of the first and second webs are aligned with an anchor while the second engagement end of each of the first and second webs are spaced apart by an actuator assembly. Springs attached to the first and second webs urge the first and second webs toward the anchor and the actuator assembly. The actuator assembly including a housing with a first end that engages the first web and a second end that engages the second web. A lever that is pivotally retained in the housing that has an actuation transmission surface on a first end that engages the first web and a second end with a first hook thereon. The actuation transmission surface transmits an actuation force from an operator into first engagement end of the first web while the housing transmits the actuation force into the first engagement surface of the second web to move first and second friction members associated with the first and second brake shoes into engagement with a drum to effect a brake application. The actuator assembly is characterized by linkage that connect a cable for communicating the actuation force from an operator to a hook on the lever of the actuator. The linkage is formed from a substantially continuous wire to define a first engagement section that is separated from a second engagement section by a center section. The continuous wire has first and second parallel legs that extend a first distance from a base of the first engagement section and thereafter converge toward a plane that is perpendicular to a center of the base to define a first loop that extends from the center section. The first loop is connected to the first hook on the lever. The parallel legs thereafter extend from the first loop along the plane for a desired length to a first tangent point to define the center section. The parallel legs thereafter extending from the first tangent point along an arcuate path for at least 135xc2x0 to a second tangent point to define a first arcuate section. The first and second legs extend from the second tangent along the tangent for a second length from the second tangent point to a third tangent point. At the third tangent point the first and second legs follow a second arcuate path toward said center section for at least 135xc2x0 until reaching a fourth tangent point to define a second arcuate section. The legs extend from the fourth tangent point along the tangent for a third distance to an end to define a second hook for the second engagement section. The end of the second hook is spaced apart from the center section by a distance that is less than a radius of for first arcuate section and as result a resilient force is required to move the end of the second hook in the plane away from the center section to receive a loop on the cable. The loop is received by the first arcuate section after expanding the end of the second hook away from the center section such that the second loop is now aligned and retained within by the first arcuate section and as a result an actuation force is substantially transmitted from the cable into the center section to move the lever in effecting a brake application.
An advantage of this invention resides in a simple wire formed linkage for joining a brake cable with a lever in an actuator for a drum-in-hat brake assembly.